1. Field of Invention
This invention pertains generally to the storage of gases and liquids and, more particularly, to an underground sequestration system and method that are particularly suitable for both long-term and short-term storage of liquids and gases such as CO2, methane, and compressed air.
2. Related Art
With the increasing concern about global warming and the presence in the atmosphere of CO2 and other heat-trapping gases, commonly known as greenhouse gases, there have been numerous efforts to find effective ways of reducing the emissions of such gases before they occur and lowering the impact of such emissions after they do occur.
CO2 is generally considered to be the biggest problem among the greenhouse gases, and by far the largest amount of man-made CO2 comes from the combustion of fossil fuels for electrical power, industrial manufacturing, and transportation. Enormous quantities of CO2 are produced during the combustion of fossil fuels, and since CO2 is a gas, it is extremely difficult to control its emission into the atmosphere.
Since coal is found and produced relatively easily in many parts of the world, including the United States, it is the leading fuel for industrial production. In the United States, coal is the most widely used fuel in the generation of electrical power, accounting for approximately 50 percent of all power produced. Natural gas has become the second most commonly used fuel in the generation of electrical power, and it now accounts for approximately 20 percent of the power produced in the United States. Coal produces by far the most CO2 per BTU of any fossil fuel, and electricity produced from coal results in three times the CO2 emissions of natural gas. Coal is currently responsible for more than 80 percent of the CO2 emissions from power generation.
Numerous political and regulatory initiatives to limit the output of CO2 are currently underway at international, national, and local levels of government. The best known of these is the international agreement known as the Kyoto Treaty in which the signatories agreed to reduce CO2 emissions below 1990 baseline levels by 2020.
One method currently employed in the reduction of CO2 emissions is carbon offsetting where, in essence, one person or entity pays another to reduce or remove global warming pollution in his name. A wide variety of offset methods are presently in use, including tree planting or reforestation, renewable energy, energy conservation, and methane capture. There are, however, serious challenges in the carbon offset market, including technical and financial difficulties encountered by many proposed projects, as well as auditing complexities. In addition, there is continuing debate over the long term effectiveness of certain offset methods, particularly reforestation.
Recycling CO2 is another method of reducing the impact of CO2 emissions that is currently evolving. Such recycling might, for example, be employed the production of industrial commodities from the stack gas effluent of coal-fired power plants, and one company has proposed to use stack gas CO2 to grow algae and then convert the algae to bio-fuel. Another proposal is to combine CO2 with hydrogen from nuclear powered electrolysis or other large sources to produce methanol which could serve as a long term energy substitute for fossil fuels. Such proposals, however, are for the most part still in the research and development stage and have not as yet been proven.
Since the oceans naturally absorb substantial amounts of CO2, some people believe that the oceans offer significant potential to sequester additional large quantities of CO2. However, ocean sequestration is ardently opposed by others on the grounds that it will not work, it will not be permanent, and that it might cause an ecological disaster.
There has also been some consideration given to sequestering CO2 in active or depleted oil and gas fields, and CO2 is currently being injected into geological formations as a stimulant for the production of oil. However, sequestering CO2 in oil and gas fields presents significant problems which will limit the degree to which this approach can effectively address the scale of the emissions reduction challenge. Oil and gas fields leak, as they are intended to do, but CO2 must be placed in secure, permanent reservoirs to effectively mitigate global warming. The injection of CO2 as to enhance production is not sequestration since much of the injected CO2 may be reproduced with the oil. Moreover, most oil and gas fields are long distances from powerhouses and other industrial sources of CO2 emissions, and long distance transport, whether by truck, by rail, or by pipeline, is very expensive.